Abstract Individuals with autism spectrum disorder (ASD) experience challenges in developing social communication and language that impact their long-term outcomes. Previous research has identified several predictors of social communication and language in children with ASD, but even when these previously-identified predictors are considered, a large amount of the variance in social communication and language ability remains unexplained. Importantly, many children with ASD do not develop effective social communication and language ability, despite receiving interventions that target these previously-identified predictors. Thus, there is a pressing need to identify novel predictors of social communication and language in ASD. It has been proposed that early differences in sensory responsiveness may arise from atypical brain states and produce ?cascading effects? on social communication and language ability. If this is the case, then intervening upon early sensory responsiveness may translate to improved social communication and language outcomes, at least in part by normalizing brain states in this population. However, evidence for this theory is limited, as the relation between sensory responsiveness in the earliest stages of development and later social communication and/or language has not been established. Additionally, the neurophysiological correlates of early and atypical sensory responsiveness have not yet been unveiled. A primary challenge to establishing these links is that ASD cannot always be definitely diagnosed in infancy and early toddlerhood. A potential solution is to prospectively follow infants at high risk for ASD. The Sensory Project in Infant/Toddler Siblings of Children with Autism (Project SPIS) represents a preliminary test of the ?cascading effects? framework in infant siblings of children with ASD (Sibs-ASD), one-third of whom will be diagnosed with ASD or language/communication impairment. NOVELTY AND IMPACT: This innovative and interdisciplinary project is expected to unveil links between a potentially tractable, but relatively understudied factor (early sensory responsivity) and social communication and language in infants at heightened risk for ASD. If our hypotheses are born out, findings will provide the basis for an RO1 that will examine the efficacy of a targeted treatment of sensory function for distal effects on social communication and language as mediated by an earlier effect on sensory responsivity in infants/toddlers at high risk for ASD. Long-term, this work may facilitate earlier identification of social communication and language impairments and point towards novel targets of early ?preventative? interventions, thereby improving long-term outcomes of children who are diagnosed with, or at risk for, ASD.